Belt Satan is the primary antagonist of the 1976 anime series Paul no Miracle Daisakusen, serving as the demonic ruler of a mysterious dimension known as the Land of Wonders or the fourth dimension. He is a giant demonic figure who had been in a deep slumber for two thousand years before awakening with the goal of conquering his own realm. His physical design is distinctive and imposing, resembling a large, dark statue with two red eyes that lack visible pupils and two horns on his head, each serving a different function; the right horn is used to channel his magical powers, while the left horn is utilized for movement.

In terms of personality, Belt Satan is depicted as tyrannical, self-righteous, and utterly ruthless. He has no tolerance for failure or betrayal, and he mercilessly destroys anyone who disobeys his orders or attempts to interfere with his plans. His primary motivation throughout the series is self-preservation and the maintenance of his power. This is directly tied to the character of Nina, a human girl whom he kidnaps in the first episode. It is revealed that Nina's life force is essential for sustaining Belt Satan's magical energy and his very existence, meaning that as long as he possesses her, he can live forever as the ruler of his world. Consequently, his actions are driven by a desperate need to retain her, making him both a powerful and a dependent villain.

Belt Satan's role in the story is to serve as the central obstacle for the young protagonist, Paul, who ventures into the demon's dimension to rescue his kidnapped friend. For the first seventeen episodes, he directly confronts Paul, attempting to eliminate the boy through various strategies and minions, all of which ultimately fail. A significant turning point occurs in episode seventeen when Paul manages to break off one of Belt Satan's horns. This injury forces the demon to retreat and hide in a location known as the Immortal Cave for the majority of the series from episode eighteen onward. Even in hiding, he continues to exert his influence by using his remaining magical horn to spy on Paul's progress through mushroom circles. His key relationships are defined by his adversarial connection with Paul and his parasitic dependency on Nina, whom he keeps imprisoned. His relationship with his own subordinates is purely transactional, based on fear and the threat of annihilation.

The character undergoes a specific arc defined by a loss and eventual return of power. After being injured and forced into hiding, he remains a passive but watchful threat for many episodes. In the final episode, he regenerates his broken horn and emerges from the Immortal Cave with his strength fully restored, unleashing natural disasters upon both the fantasy world and the real world to demonstrate his regained might. However, his overconfidence proves to be his undoing. While gloating over his overwhelming power and causing chaos, he leaves himself vulnerable. Paul throws his yo-yo, Nina throws her necklace, and another character named Pippi throws her necklace as well; these three objects strike and destroy both of his horns, causing him to burst into flames and finally die.

Belt Satan possesses several notable abilities. His magic is primarily channeled through his horns, especially the right one, allowing him to cast spells and maintain his influence over his dimension. He frequently employs telekinetic abilities, using what appears to be a force grip to retrieve Nina whenever she is rescued by Paul, and can also generate powerful lightning or whirlwinds to attack his enemies. His connection to Nina is perhaps his most crucial but passive ability, as her vitality is the source of his life and magical power, creating a symbiotic relationship that defines his every action.